This invention relates to an internal combustion engine having a sensor-monitored secondary air charging system. This invention further relates to a method of measuring the operating condition of an internal combustion engine.
Devices of the type described above are known, for example, from Weber et al., U.S. Pat. No. 6,094,909 (=WO 97/38 212). According to FIG. 8 of that document, a secondary air injection system is proposed for an internal combustion engine, comprising a turbine unit 114 and a compressor 113. The turbine is driven via a bypass line arranged in parallel with the throttle valve 115 in the intake tract. In addition, at least one throttle member 120 is also situated in the bypass line to the turbine. Intake air flow and secondary air flow are adjusted simultaneously by the interaction of throttle valve 115 and throttle member 120. The output of the turbine 114 and thus also the secondary air delivered by the compressor 113 as well as the intake air flow delivered as the addition to the air streams can be adjusted through the throttle member 120 and the throttle valve 115. Instead of the regulated turbine, it is of course also possible for a different drive to be provided for the compressor, e.g., an electric motor.
For optimum adjustment of the two air streams, the complex processes involved in an internal combustion engine must be understood. The air demand prevailing in the intake tract of the internal combustion engine and/or in the exhaust system can be determined from this. The air demand by the internal combustion engine depends on the load condition, for example, but also on the type of operation desired, e.g., combustion of fuel in an oxygen excess or in a lack of oxygen. Secondary air is introduced into the exhaust gas system, e.g., in the cold start phase of the engine. The exhaust gas system should oxidize any incompletely burned constituents of the exhaust, and in addition the downstream catalytic converter in the exhaust system should be heated by this exothermic reaction. This decreases cold-start emissions and shortens the cold start phase, because due to this heating the catalytic converter begins to be effective sooner.
When the secondary air is introduced, a certain air ratio must be established in order for emission abatement to function properly. If there is too much secondary air, the exhaust is cooled too greatly without the additional exhaust components being oxidized. If there is too little secondary air, not enough oxygen is available for oxidation of the exhaust constituents. Therefore, the air flow rate through the secondary air charging system must be monitored.
According to Bayerle et al., U.S. Pat. No. 5,921,077 (=EP 800,611), a method is disclosed whereby the air flow rate delivered by the secondary air pump is determined by an air flow rate sensor, and the resulting value is used to control the secondary air pump. However, the use of air flow rate sensors has some significant disadvantages. First, these measurement devices are quite expensive, so that the economics of this proposed solution are adversely affected. In addition, they are highly sensitive to fouling, so the air flow rate values determined may be inaccurate. This has a direct effect on the desired exhaust gas result to be achieved with the internal combustion engine.